//
//  Copyright (c) 2022 Touch Instinct
//
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//  of this software and associated documentation files (the Software), to deal
//  in the Software without restriction, including without limitation the rights
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//  copies of the Software, and to permit persons to whom the Software is
//  furnished to do so, subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in
//  all copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED AS IS, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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//  THE SOFTWARE.
//

import Foundation

private final class MapAsyncOperation<Output, Failure: Error>: AsyncOperation<Output, Failure> {
    private var dependencyObservation: NSKeyValueObservation?

    public init<DependencyOutput, DependencyFailure: Error>(dependency: AsyncOperation<DependencyOutput, DependencyFailure>,
                                                            mapOutput: @escaping (DependencyOutput) -> Result<Output, Failure>,
                                                            mapFailure: @escaping (DependencyFailure) -> Failure) {

        super.init()

        cancelOnCancellation(of: dependency)

        dependencyObservation = dependency.subscribe { [weak self] in
            switch mapOutput($0) {
            case let .success(result):
                self?.handle(result: result)

            case let .failure(error):
                self?.handle(error: error)
            }
        } onFailure: { [weak self] in
            self?.handle(error: mapFailure($0))
        }

        addDependency(dependency) // keeps strong reference to dependency as well

        state = .isReady
    }
}

public extension AsyncOperation {
    func map<NewOutput, NewFailure: Error>(mapOutput: @escaping (Output) -> Result<NewOutput, NewFailure>,
                                           mapFailure: @escaping (Failure) -> NewFailure)
    -> AsyncOperation<NewOutput, NewFailure> {

        MapAsyncOperation(dependency: self,
                          mapOutput: mapOutput,
                          mapFailure: mapFailure)
    }

    func map<NewOutput>(mapOutput: @escaping (Output) -> NewOutput) -> AsyncOperation<NewOutput, Failure> {
        MapAsyncOperation(dependency: self,
                          mapOutput: { .success(mapOutput($0)) },
                          mapFailure: { $0 })
    }
}